Many components of the IS are constructed as modular units which do not need
to communicate with each other such that the number of components increases but
the size remains constant. However, a sub-modular IS architecture in which
lymph node number and size both increase sublinearly with body size is shown to
efficiently balance the requirements of communication and migration, consistent
with experimental data. We hypothesize that the IS architecture optimizes the
tradeoff between local search for pathogens and global response using
antibodies.